Recently, many people, young ladies among others, have worried about conspicuous pores and have demanded a skin preparation for external use for making the pore inconspicuous. However, the mechanism for making the pore conspicuous has not been elucidated yet, and use of an astringent lotion and excision of parakeratosis have been usual treatments of parakeratosis. Or the skin problem has been often covered apparently by means of foundation cream. The astringent lotion is used to tighten the skin, and the action thereof is to temporarily reduce the temperature of the skin surface with alcohol, or to coagulate proteins with organic acids and the like. Accordingly, the skin suffers a great burden since the skin is temporarily tightened without fundamentally solving the problem of conspicuous pores, and the effect of the astringent lotion has been insufficient.
On the other hand, it has been reported that the derivatives of glycolic acid and ascorbic acid have the effect of pore shrinking (see, for example non-patent reference #1). The mechanism of action and the extent of effect thereof are still unknown.
Excision of keratin plug is to physically remove the keratin plug. Some known methods of excision include parakeratosis remover containing a high molecular weight compound having salt-generating groups (see, for example, patent reference #1), cosmetics containing water-insoluble cyclodextrin polymers (see, for example, patent reference #2), keratin plug remover cosmetics containing not less than 50 weight % of oil having a coefficient of viscosity of 5 to 80 mPa·s/25 degrees centigrade (see, for example, patent reference #3). Physical removal of the keratin plug may damage the skin by a physical force, and side effects on the skin have been a problem. The effect of this method is not always satisfactory since the effect thereof is temporary and keratin plug is readily regenerated, and removal of keratin plug may only expand the pore.
The inventors of the present invention have made intensive studies on the mechanism of generating the conspicuous pores in order to develop a skin preparation for external use that exhibits capabilities of ameliorating the conspicuous pores, and found and reported at the 102nd annual meeting of Japan Society of Dermatology (see non-patent reference #2) that:
(1) the conically recessed portion around the pore is recognized as pore, and the pores become conspicuous if this portion is wider;
(2) the skin surface stratum corneum of the conical portion is in a state of parakeratosis (there remains nucleus which should have disappeared);
(3) those person having conspicuous pore excretes a lot of sebum, in particular unsaturated fatty acids;
(4) the unsaturated fatty acids cause the parakeratosis; and
(5) the conspicuous pore is likely to be caused by the unsaturated fatty acids contained in the sebum.
The inventors of the present invention have elucidated that the mechanism of developing conspicuous pore may be partly due to parakeratosis caused by the sebum. The inventors have also elucidated that the amelioration of parakeratosis may lead to the amelioration of conspicuous pores.    Patent reference #1: JP-A-H05-97627    Patent reference #2: JP-A-H05-105619    Patent reference #3: JP-A-2002-241260    Non-patent reference #1: Yazawa, et al., Fragrance Journal, 2002, vol. 30, No. 2, pp. 54-58    Non-patent reference #2: Iida, et al., 102nd annual meeting programs and abstract, 2003, 103, pp. 846